System and method for leak detection in external cooling pad

ABSTRACT

An externally-applied heat exchange pad has three layers laminated together, an inner and outer non-conductive layer and a middle conductive layer. A leak in the inner layer causes coolant to contact the middle layer and change impedance, which can be sensed and used as an indication of an impending total leak of the pad.

This is a continuation of and claims priority to U.S. patent applicationSer. No. 11/181,122, filed Jul. 14, 2005, now U.S. Pat. No. 7,951,182.

FIELD OF THE INVENTION

The present invention relates generally to patient temperature controlusing externally-applied devices.

BACKGROUND OF THE INVENTION

Patient temperature control systems have been introduced to preventfever in patients in the neuro ICU due to suffering from sub-arachnoidhemorrhage or other neurologic malady such as stroke. Also, such systemshave been used to induce mild or moderate hypothermia to improve theoutcomes of patients suffering from such maladies as stroke, cardiacarrest, myocardial infarction, traumatic brain injury, and highintracranial pressure. The present assignee has covered one or more ofthe above treatments using an intravascular heat exchange catheter inU.S. Pat. Nos. 6,149,670, 6,290,717, 6,432,124, 6,454,793, 6,682,551,and 6,726,710 (collectively, “the Alsius treatment patents”), all ofwhich are incorporated herein by reference.

Less optimally, external patient temperature control systems may beused. Such systems are disclosed in U.S. Pat. Nos. 6,827,728, 6,818,012,6,802,855, 6,799,063, 6,764,391, 6,692,518, 6,669,715, 6,660,027,6,648,905, 6,645,232, 6,620,187, 6,461,379, 6,375,674, 6,197,045, and6,188,930 (collectively, “the external pad patents”), all of which areincorporated herein by reference. Because such systems are used, thepresent invention recognizes the need to detect impending coolant leaksin the applied pads to avoid such leaks, so that patient discomfort andsystem malfunction are avoided before they occur.

SUMMARY OF THE INVENTION

A heat exchange pad configured for placement against the skin of apatient to exchange heat with the patient includes an outer envelope.The outer envelope includes an outer layer made of a high dielectricmaterial such that any electrical discharge in the pad is effectivelyblocked from passing through the outer layer to the patient. Also, theenvelope has an inner layer. A middle layer is sandwiched between theinner and outer layers and is made of a relatively electricallyconductive material. The middle layer is electrically connected to acontrol system associated with the pad.

If desired, the layers can be laminated together. In some embodiments,in the event of a rupture in the inner layer, coolant in the padcontacts the middle layer to establish a change in impedance that may besensed by the control system. In specific embodiments an impedancebetween the middle layer and the coolant can be used as an indication asto whether a leak exists. More particularly, in some implementations adrop in impedance can indicate that a leak is in the inner layer. Theinner layer may be made of the same material as the outer layer, and themiddle layer may be foil or plastic impregnated with conductivematerial.

In another aspect, a patient temperature control system includes atleast one pad positionable against the skin of a patient to exchangeheat therewith, and a control system engaged with the pad to circulatecoolant therethrough to establish a desired temperature. Means areprovided on the pad for providing early warning of a complete loss ofintegrity of the pad before it occurs.

In still another aspect, a method for providing an alarm that indicatesan impending loss of fluid integrity of a heat exchange pad engageablewith the exterior of a patient before fluid in the pad leaks out of thepad onto the patient includes receiving a signal from the padrepresenting an impedance. If the signal satisfies a leakage threshold,an alarm is activated.

The details of the present invention, both as to its structure andoperation, can best be understood in reference to the accompanyingdrawings, in which like reference numerals refer to like parts, and inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a non-limiting system in accordance withthe present invention; and

FIG. 2 is a cross-section of a non-limiting embodiment of the presentexternal heat exchange pad.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, a system is shown, generally designated10, that includes one or more pads 12 that are positioned against theexternal skin of a patient 14 (only one pad 12 shown for clarity). Thepad 12 may be any one of the pads disclosed in the external pad patentsor it may be any other type of external heat exchange pads, as modifiedas disclosed herein in reference to FIG. 2. A substrate 16 such as alabel that is affixed to the pad or an instruction manual thataccompanies the pad can also be provided that bears instructions foruse. In any case, the temperature of the pad 12 can be controlled by acontroller 18 receiving a patient temperature signal from one or moretemperature sensors “S” in accordance with principles set forth in theexternal pad patents to exchange heat with the patient 14, including toestablish normothermia in a febrile patient and to induce therapeuticmild or moderate hypothermia in the patient in response to the patientpresenting with, e.g., cardiac arrest, myocardial infarction, stroke,high intracranial pressure, traumatic brain injury, or other malady theeffects of which can be ameliorated by hypothermia. Patient warming can,also be effected using the pad 12 for, e.g., re-warming after surgery.

Heat exchange fluid, referred to herein as “coolant” regardless of itstemperature, is circulated from the control system 18, through a supplyline 20 to the pad 12, through various internal coolant circulationstructure within the pad 12, e.g., the structures disclosed in the padpatents, and back through a return line 22 to the control system 18 forheating or cooling as needed for the particular application. Electricalleads 24, e.g., two, can be provided with one lead 24 extending betweenthe external three-ply case of the pad 12 and the control system 18 andthe other lead 24 extending between the interior coolant space of thepad 24 and the control system 18, for purposes to be shortly disclosedin relation to FIG. 2. A pump in or associated with the control system18 may be engaged with the coolant supply line 20 to push coolantthrough the pad 12, or the pump may be engaged with the coolant returnline 22 to suck coolant through the pad 12.

FIG. 2 shows details of the invention. The pad 12 includes an outerenvelope 26 that holds internal coolant circulation structure, which isomitted in FIG. 2 for clarity of disclosure. The outer envelope 26 isthree-ply at least. Specifically, the envelope 26 includes an outerlayer 28 made of a high dielectric material so that any electricaldischarge in the pad 12 is effectively blocked from passing through theouter layer 28 to the patient, it being understood that the outer layer28 is disposed against the skin of the patient perhaps with a gel orliquid interposed between it and the skin. The envelope 26 also has aninner layer 30 that may be made of the same material as the outer layer28. A middle layer 32 is sandwiched between the inner and outer layers30, 28. The middle layer 32 may be made of a relatively electricallyconductive material, e.g., foil, or plastic impregnated with sufficientconductive material, or other appropriate material, and it iselectrically connected to one of the electrical leads 24 and, hence, tothe control system 18. The other lead extends between the control system18 and interior coolant space 34 of the pad 12 as shown. The layers 28,30, 32 preferably are laminated together or otherwise held togetheragainst each adjacent layer.

The point is that the middle layer 32 is sufficiently conductive suchthat in the event of a rupture in the inner layer 30, coolant contactsthe middle layer 32 to establish a change in impedance that is sensed byan impedance measurement/detector system 36 through the leads 24. Theimpedance measurement/detector system 36 may be part of the controlsystem 18 shown in FIG. 1.

For instance, the impedance between the middle layer 32 and the coolantmay be measured through the leads 24 as an indication as to whether aleak exists. As an example, a significant drop in impedance can indicatea leak in the inner layer 30, making a leak through all three layersmore likely than otherwise and, hence, providing early warning of such acomplete loss of integrity of the pad 12 before it occurs. Accordingly,the control system 18 may activate an audible and/or visual alarm 38(FIG. 1) to alert personnel of an impending leak. The same principlescan be applied to determining whether the liquid or gel, if used, thatis between the patient and pad is leaking through a hole in the outerlayer to the middle layer.

While the particular SYSTEM AND METHOD FOR LEAK DETECTION IN EXTERNALCOOLING PAD as herein shown and described in detail is fully capable ofattaining the above-described objects of the invention, it is to beunderstood that it is the presently preferred embodiment of the presentinvention and is thus representative of the subject matter which isbroadly contemplated by the present invention, that the scope of thepresent invention fully encompasses other embodiments which may becomeobvious to those skilled in the art, and that the scope of the presentinvention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more”. It is not necessary for a device or method toaddress each and every problem sought to be solved by the presentinvention, for it to be encompassed by the present claims. Furthermore,no element, component, or method step in the present disclosure isintended to be dedicated to the public regardless of whether theelement, component, or method step is explicitly recited in the claims.Absent express definitions herein, claim terms are to be given allordinary and accustomed meanings that are not irreconcilable with thepresent specification and file history.

1. A patient temperature control system, comprising: at least one padpositionable against the skin of a patient to exchange heat therewith; acontrol system engaged with the pad to circulate coolant therethrough toestablish a desired temperature; and the pad including an envelopedefined by an outer non-conducting layer, an inner non-conducting layer,and a middle conducting layer sandwiched therebetween, the middleconducting layer being electrically connected to the control system toprovide a signal thereto representing whether a leak has occurredthrough either one of the non-conducting layers.
 2. The system of claim1, wherein the layers are laminated together.
 3. The system of claim 1,comprising an impedance detection system communicating with at least aportion of the pad, wherein in the event of a rupture in the innerlayer, coolant in the pad contacts the middle layer to establish achange in impedance that is sensed by the impedance detection system. 4.The system of claim 3, wherein the impedance detection system uses animpedance between the middle layer and the coolant as an indication asto whether a leak exists.
 5. The system of claim 4, wherein theimpedance detection system correlates a drop in impedance to a leak inthe inner layer.
 6. The system of claim 1, wherein the inner layer ismade of the same material as the outer layer.
 7. The system of claim 1,wherein the middle layer is made of foil.
 8. The system of claim 1,wherein the middle layer is made of plastic impregnated with conductivematerial.